1. Field of the Invention
The present invention relates to fumigants, and particularly to fumigant compositions having similar properties to methyl bromide, without its ozone-depleting properties. Specifically, the invention relates to azeotropic and azeotrope-like compositions of methyl iodide and at least one fluorocarbon or hydrofluorocarbon, such as 1,1,1,3,3-pentafluoropropane (HFC-245fa).
2. Description of the Related Art
Methyl Bromide is a gaseous fumigant that has been used commercially since the early 1900's. It is known for being extremely effective as a herbicide, nematocide, insecticide and fungicide. Methyl bromide has been widely used for soil fumigation, not only for controlling a variety of pests on numerous crops, but also as a commodity quarantine treatment for imports and exports, and as a structural fumigant applied to a building surface or the like. However, it is a Restricted Use Pesticide (RUP) because of its high acute toxicity to applicators. Methyl bromide has also been designated as an ozone-depleter, and thus its production and use have been severely restricted pursuant to the Montreal Protocol.
Efforts have been made to develop an alternative or replacement for methyl bromide as a fumigant. There currently exist only a few conventional methyl bromide alternatives, such as chloropicrin, 1,3-dichloropropene, metham sodium, and methyl iodide. Two or more of these materials are commonly applied as a mixture, to produce a product similar to methyl bromide. However, none of these potential alternatives are an adequate “drop-in replacement” for methyl bromide, based on their physical handling requirements, performance, or economics. The term “drop-in replacement” is used when the methodology, equipment, production system, and the like, of an original material do not have to be changed significantly when using a replacement material, and that a comparable amount of the replacement material can be used for the same targets as the original material.
A great deal of research has been conducted in evaluating methyl iodide as a drop-in replacement for methyl bromide. Methyl iodide has been found to be equal to or better than methyl bromide in combating weeds, nematodes, and soil pathogens. Further, methyl iodide is not associated with ozone depletion, and does not result in plant toxicity when used in effective concentrations. However, methyl iodide is a low boiling liquid with a boiling point of 42.5° C. (108° F.), while methyl bromide is a gas at ambient temperature and pressure. Methyl iodide has a lower vapor pressure and higher density than methyl bromide. Thus, the use of methyl iodide in existing methyl bromide equipment suffers several shortcomings such as clogged tubing, material remnants in system pipes, and long line purging processes for cleaning. Furthermore, the use of methyl iodide results in problems such as missed bed applications, since the methyl bromide equipment is designed for gaseous fumigant applications. Such missed bed applications may lead to significant crop loss in soil fumigation. Thus, while methyl iodide may serve well as a fumigant, it is not a suitable drop-in replacement for methyl bromide.
It would be desirable to provide a fumigant alternative to methyl bromide which can also serve as a drop-in replacement, thereby allowing for the use existing methyl bromide equipment and systems. The present invention provides a solution to this problem.
It has now been unexpectedly found that by combining methyl iodide with at least one fluorocarbon or hydrofluorocarbon, the resulting azeotropic or azeotrope-like composition exists as a gas at temperatures below about 30° C. The resulting gaseous composition serves as a drop-in replacement for methyl bromide, providing benefits if a methyl iodide fumigant while also utilizing existing methyl bromide equipment.